Numerous technologies for welding of plastic pipes are known in the art, and depending on the particular pipe requirements or size, various welding methods may be employed. For example, where relatively constant welding temperature is desired, induction welding may be employed. On the other hand, where relatively fast weld and/or cool times are desired, vibration welding may be used. In further applications, where relatively small diameter pipes are welded, electrofusion welding may be employed while butt fusion welding may be especially appropriate for larger diameter pipes.
However, despite the relatively large variety in welding techniques for polymeric materials, validation of the weld quality remains often problematic. Particularly, all or almost all of the known methods for determination of the quality of welds for HDPE (high-density polyethylene) piping exhibit significant problems. For example, the test procedure described in ASTM F600-78 was withdrawn in 1991 because successful inspection techniques as well as subsequent interpretation of the examination results was too dependent on the skill of the operator. Consequently, current industry practice relies in many cases at least in part on visual examination of the exterior weld bead to determine the weld quality. However, field experience frequently shows that there are often substantial inconsistencies between the visual weld bead quality and actual weld integrity.
In another example (e.g., currently known quality control (QC) technique of bend strap tests, as exemplified in ASTM D2657-97), other limitations to ensuring fusion quality are often found. Typically, if a fusion defect is not common to the entire weld, then probability of selecting the defective region of the weld is low. For example, a 30 inch diameter, DR 13.5 (2.22 inch wall) weld has a 3.33 inch sample thickness requirement. Assuming the defect is about 10% of the circumference, then the probability of selecting the defective area is less than 15%. This percentage is further reduced if a random inspection is completed and it is unknown if the weld is defective. Further assuming that about 10% of all welds in the population contain defects, then the probability of finding the defective area of a defective weld is reduced to less than 1.5%.
In still further known methods, ultrasonic testing may be employed in a pulse-echo system to test for various defects in a polymer pipe and/or pipe weld. Ultrasound testing is typically rapid and non-destructive, and relatively inexpensive. However, currently known ultrasound methods are generally limited to relatively thin walls (i.e., less than ¾ inch). Moreover, currently known ultrasonic methods will most likely not detect lack of fusion (LOF) in a butt weld.
To overcome at least some of the disadvantages of visual testing, ultrasonic testing, or random inspection, assembled polymer pipes may be pressurized with a fluid and tested for leakage. However, integrity of a polymer piping system is generally not completely assured using a short-term pressure-leak test (e.g., hydro-tests) due to the viscoelastic nature of the polymer. Whereby, deformational response of the assembled pipe to applied stress depends on both time and material temperature. Therefore, short-term pressure leak tests ensure the absence of leaks in a piping system and are generally not employed to test the strength of plastic piping systems or to ensure long-term life expectancy. Moreover, while some of the recently developed tests improve identification of certain defects at to some extent, all or almost all of such tests need to be performed with non-operational pipelines.
Thus, although there are numerous methods for testing polymer pipes and pipe welds known in the art, all or almost all of them suffer from one or more disadvantages. Still further, most known systems will provide conclusive results only in non-operational pipelines. Therefore, there is still a need to provide improved methods and configurations for testing polymer pipes and pipe welds known in the art, and especially for pipelines that are already in operation.